Memory devices

ABSTRACT

A memory device includes a first cell block on a substrate at a first level, and a second cell block on the substrate at a second level different from the first level. Each of the first and second cell blocks includes a word line extending in a first direction that is parallel to a top surface of the substrate, a word line contact connected to a center point of the word line, a bit line extending in a second direction that is parallel to the top surface of the substrate and intersects the first direction, a bit line contact connected to a center point of the bit line, and a memory cell between the word and bit lines. The second cell block is offset from the first cell block in at least one of the first and second directions.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/168,153, filed Oct. 23, 2018, which claims the benefit of KoreanPatent Application No. 10-2017-0164331, filed on Dec. 1, 2017, in theKorean Intellectual Property Office, the disclosures of which areincorporated herein in their entireties by reference.

BACKGROUND

The inventive concept relates to memory devices, and, more particularly,to memory devices having a cross point array structure.

As electronic products become smaller with reduced weights, thicknesses,and sizes, the demand for high integration densities of memory devicesmay increase. High integration density memory devices may use athree-dimensional (3D) cross point structure in which memory cells areprovided at cross points between two electrodes. When memory devices arestacked in two or more layers, a wiring resistance or an area of awiring connection region of the memory devices may increase.

SUMMARY

Embodiments of the inventive concept may provide a cross-point-arraymemory device having a relatively low wiring resistance and a relativelycompact size.

According to some embodiments of the inventive concept, there isprovided a memory device including a first cell block on a substrate ata first level, and a second cell block on the substrate at a secondlevel different from the first level, wherein each of the first andsecond cell blocks includes a word line extending in a first directionthat is parallel to a top surface of the substrate, a word line contactconnected to a center point of the word line, a bit line extending in asecond direction that is parallel to the top surface of the substrateand intersects the first direction, a bit line contact connected to acenter point of the bit line, and a memory cell between the word lineand the bit line, and wherein the second cell block is offset from thefirst cell block in at least one of the first and second directions.

According to other embodiments of the inventive concept, there isprovided a memory device including a first cell block on a substrate, asecond cell block on the first cell block, a third cell block on thesecond cell block, and a fourth cell block on the third cell block,wherein each of the first to fourth cell blocks includes a word lineextending in a first direction that is parallel to a top surface of thesubstrate, a word line contact connected to a center point of the wordline, a bit line extending in a second direction that is parallel to thetop surface of the substrate and intersects the first direction, a bitline contact connected to a center point of the bit line, and a memorycell between the word line and the bit line, and wherein at least one ofthe first to fourth cell blocks is offset from another of the first tofourth cell blocks in at least one of the first and second directions.

According to further embodiments of the inventive concept, there isprovided a memory device including a first cell block on a substrate ata first level, a second cell block on the substrate at a second leveldifferent from the first level, a third cell block on the substrate at athird level different from the first and second levels, and a fourthcell block on the substrate at a fourth level different from the firstto third levels, wherein each of the first to fourth cell blocksincludes a first sub cell array region and a second sub cell arrayregion spaced apart from each other in a first direction that isparallel to a top surface of the substrate, and a third sub cell arrayregion and a fourth sub cell array region respectively spaced apart fromthe first and second sub cell array regions in a second direction thatintersects the first direction, and wherein the first to fourth cellblocks are offset from each other in at least one of the first andsecond directions.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the inventive concept will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is an equivalent circuit diagram of a memory device according toexample embodiments of the inventive concept;

FIG. 2A is an exploded perspective view of a memory device according toexample embodiments of the inventive concept;

FIG. 2B is an exploded perspective view of a memory device according tofurther example embodiments of the inventive concept;

FIG. 2C is an exploded perspective view of a memory device according tofurther example embodiments of the inventive concept;

FIG. 3 is a perspective view of a memory device according to exampleembodiments of the inventive concept;

FIGS. 4 to 7 are top layout views of first cell blocks, second cellblocks, third cell blocks, and fourth cell blocks of FIG. 3,respectively;

FIG. 8 is a cross-sectional view taken along line A1-A1′ of FIGS. 4 to7;

FIG. 9 is a cross-sectional view taken along line B1-B1′ of FIGS. 4 to7;

FIGS. 10 to 14 are cross-sectional views of memory cells according toexample embodiments of the inventive concept;

FIG. 15 is a top layout view of a memory device according to exampleembodiments of the inventive concept;

FIG. 16 is a cross-sectional view of a memory device according toexample embodiments of the inventive concept;

FIGS. 17 and 18 are cross-sectional views of a memory device accordingto example embodiments of the inventive concept;

FIGS. 19 and 20 are cross-sectional views of a memory device accordingto further example embodiments of the inventive concept; and

FIGS. 21 and 22 are cross-sectional views of a memory device accordingto further example embodiments of the inventive concept.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the inventive concept will be described indetail with reference to the attached drawings. Like reference numberssignify like elements throughout the description of the figures. It isnoted that aspects of the invention described with respect to oneembodiment, may be incorporated in a different embodiment although notspecifically described relative thereto. That is, all embodiments and/orfeatures of any embodiment can be combined in any way and/orcombination.

Some embodiments of the inventive concept stem from a realization thatmemory devices that include a plurality of sequentially stacked cellblocks may be interconnected via bit line contacts and/or word linecontacts in which the interconnection lines are disposed outside of thefootprint of the cell blocks in a plan view of the memory device. Thismay result in increased wiring resistance along with a larger footprintfor the memory device. According to some embodiments of the inventiveconcept, a memory device may include a plurality of stacked cell blocksin which each cell block is offset in at least one direction from anadjacent cell block. The offset may provide pathways to run bit linesand/or word lines between the cell blocks without running lines outsidethe overall perimeter of the memory device when viewed in a plan view.This may reduce the overall length of the bit lines and/or word linesand, as a result, reduce wiring resistance. Improvements in electricalcharacteristics, such as voltage drops associated with the wiring mayalso be provided. Because the wiring connections for the bit linesand/or word lines are within the footprint of the cell blocks in a planview of the memory device, the overall device footprint may be reduced.

FIG. 1 is an equivalent circuit diagram of a memory device 10 accordingto example embodiments of the inventive concept.

Referring to FIG. 1, the memory device 10 may include lower word linesWL11 and WL12 extending in a first direction (e.g., the X direction ofFIG. 1) and spaced apart from each other in a second directionperpendicular to or intersects with the first direction (e.g., the Ydirection of FIG. 1), and upper word lines WL21 and WL22 provided on thelower word lines WL11 and WL12, spaced apart from the lower word linesWL11 and WL12 in a third direction perpendicular to or intersects withthe first direction (e.g., the Z direction of FIG. 1), and extending inthe first direction. The memory device 10 may further include bit linesBL1, BL2, BL3, and BL4 provided between the lower word lines WL11 andWL12 and the upper word lines WL21 and WL22, spaced apart from the lowerword lines WL11 and WL12 and the upper word lines WL21 and WL22 in thethird direction, and extending in the second direction.

First memory cells MC1 may be provided between the lower word lines WL11and WL12 and the bit lines BL1, BL2, BL3, and BL4, and second memorycells MC2 may be provided between the bit lines BL1, BL2, BL3, and BL4and the upper word lines WL21 and WL22. Specifically, the first andsecond memory cells MC1 and MC2 may include variable resistance materiallayers RM for storing data and switching devices SW for selecting amemory cell. The switching devices SW may also be referred to asselection devices or access devices.

In example embodiments, the first and second memory cells MC1 and MC2may be provided to have symmetrical structures in the third direction.For example, as illustrated in FIG. 1, in the first memory cells MC1,the variable resistance material layers RM may be connected to the bitlines BL1, BL2, BL3, and BL4, the switching devices SW may be connectedto the lower word lines WL11 and WL12, and the variable resistancematerial layers RM may be connected in series to the switching devicesSW. In the second memory cells MC2, the variable resistance materiallayers RM may be connected to the bit lines BL1, BL2, BL3, and BL4, theswitching devices SW may be connected to the upper word lines WL21 andWL22, and the variable resistance material layers RM may be connected inseries to the switching devices SW.

However, embodiments of the inventive concept are not limited thereto.Unlike FIG. 1, the locations of the variable resistance material layersRM and the switching devices SW may be switched in the first and secondmemory cells MC1 and MC2. For example, in the first memory cells MC1,the variable resistance material layers RM may be connected to the lowerword lines WL11 and WL12, and the switching devices SW may be connectedto the bit lines BL1, BL2, BL3, and BL4. In the second memory cells MC2,the variable resistance material layers RM may be connected to the upperword lines WL21 and WL22, and the switching devices SW may be connectedto the bit lines BL1, BL2, BL3, and BL4.

In other embodiments, the first and second memory cells MC1 and MC2 maybe provided to have similar or identical structures. Unlike FIG. 1, inthe first memory cells MC1, the variable resistance material layers RMmay be connected to the bit lines BL1, BL2, BL3, and BL4, and theswitching devices SW may be connected to the lower word lines WL11 andWL12. In the second memory cells MC2, the variable resistance materiallayers RM may be connected to the upper word lines WL21 and WL22, andthe switching devices SW may be connected to the bit lines BL1, BL2,BL3, and BL4.

Unlike FIG. 1, additional bit lines (not shown) and additional wordlines (not shown) may be further provided on the upper word lines WL21and WL22, and additional memory cells may be further provided betweenthe upper word lines WL21 and WL22 and the additional bit lines andbetween the additional bit lines and the additional word lines.

Methods of driving the memory device 10, according to some embodimentsof the inventive concept, will now be described.

For example, a voltage may be applied to the variable resistancematerial layers RM of the first and second memory cells MC1 and MC2through the lower and upper word lines WL11, WL12, WL21, and WL22 andthe bit lines BL1, BL2, BL3, and BL4, such that a current may flowthrough the variable resistance material layers RM. For example, thevariable resistance material layers RM may include phase change materiallayers capable of reversibly transitioning between a first state and asecond state. Embodiments of the variable resistance material layers RM,however, are not limited thereto, and may include any variable resistor,in which a resistance value varies depending on an applied voltageapplied thereto and/or a current received therethrough. For example, theresistance of the variable resistance material layers RM may reversiblytransition between the first state and the second state based on thevoltage applied to the variable resistance material layer RM of aselected first or second memory cell MC1 or MC2.

Based on the variation in the resistance of the variable resistancematerial layers RM, digital data, such as “0” or “1,” may be stored inor erased from the first and second memory cells MC1 and MC2. Forexample, data corresponding to a high-resistance state “0” and alow-resistance state “1” may be programmed in the first and secondmemory cells MC1 and MC2. Herein, a program operation from thehigh-resistance state “0” to the low-resistance state “1” may bereferred to as a “set operation,” and a program operation from thelow-resistance state “1” to the high-resistance state “0” may bereferred to as a “reset operation.” It will be understood, however, thatthe first and second memory cells MC1 and MC2, according to variousembodiments of the inventive concept, are not limited to theabove-described digital data of the high-resistance state “0” and thelow-resistance state “1,” and may store data based on various resistancestates.

An arbitrary first or second memory cell MC1 or MC2 may be addressed byselecting one of the lower and upper word lines WL11, WL12, WL21, andWL22 and one of the bit lines BL1, BL2, BL3, and BL4, and may beprogrammed by applying a signal between the lower or upper word lineWL11, WL12, WL21, or WL22 and the bit line BL1, BL2, BL3, or BL4, anddata based on a resistance value of a variable resistor of the first orsecond memory cell MC1 or MC2 may be read by measuring a current valuethrough the bit line BL1, BL2, BL3, or BL4.

According to example embodiments, the lower word lines WL11 and WL12 andthe upper word lines WL21 and WL22 may be vertically spaced apart fromeach other by providing the bit lines BL1, BL2, BL3, and BL4therebetween, the first memory cells MC1 may be provided between the bitlines BL1, BL2, BL3, and BL4 and the lower word lines WL11 and WL12, andthe second memory cells MC2 may be provided between the bit lines BL1,BL2, BL3, and BL4 and the upper word lines WL21 and WL22. Therefore, thememory device 10, according to some embodiments of the inventiveconcept, may have a relatively compact size and a relatively highintegration density.

FIG. 2A is an exploded perspective view of a memory device 10A accordingto example embodiments of the inventive concept.

Referring to FIG. 2A, the memory device 10A may include first to fourthcell blocks BF1, BF2, BF3, and BF4 located on a substrate 110 atdifferent levels. Each of the first to fourth cell blocks BF1, BF2, BF3,and BF4 may include the lower word lines WL11 and WL12 (see FIG. 1), thebit lines BL1, BL2, BL3, and BL4 (see FIG. 1), and the first memorycells MC1 (see FIG. 1) provided between the lower word lines WL11 andWL12 and the bit lines BL1, BL2, BL3, and BL4, as illustrated in FIG. 1.

For example, as illustrated in FIG. 2A, the first cell block BF1 may beprovided at a first level LV1 and the second cell block BF2 may beprovided at a second level LV2 on the substrate 110. The second cellblock BF2 may be located so as to partially overlap with the first cellblock BF1. For example, the second cell block BF2 may be provided at alocation shifted or offset from the first cell block BF1 in a firstdirection (e.g., the X direction) by ½ of a first width W1 of the firstcell block BF1 in the first direction.

The third cell block BF3 may be provided at a third level LV3 on thesubstrate 110. The third cell block BF3 may be located so as topartially overlap with both of the first and second cell blocks BF1 andBF2. For example, the third cell block BF3 may be provided at a locationshifted or offset from the first cell block BF1 in the first directionby ½ of the first width W1 of the first cell block BF1, and in a seconddirection (e.g., the Y direction) by ½ of a second width W2 of the firstcell block BF1 in the second direction. In addition, the third cellblock BF3 may be provided at a location shifted or offset from thesecond cell block BF2 by ½ of the second width W2 in the seconddirection.

The fourth cell block BF4 may be provided at a fourth level LV4 on thesubstrate 110. The fourth cell block BF4 may be located so as topartially overlap with all of the first to third cell blocks BF1, BF2,and BF3. For example, the fourth cell block BF4 may be provided at alocation shifted or offset from the first cell block BF1 by ½ of thesecond width W2 in the second direction. In addition, the fourth cellblock BF4 may be provided at a location shifted or offset from the thirdcell block BF3 by ½ of the first width W1 in the first direction.

A driving circuit region DR, including driving circuits for separatelydriving the first to fourth cell blocks BF1, BF2, BF3, and BF4, may beprovided at a fifth level LV5 on the substrate 110. For example, a firstword line driving region DR_WL1, a second word line driving regionDR_WL2, a first bit line driving region DR_BL1, and a second bit linedriving region DR_BL2 may be provided on the substrate 110. The drivingcircuits may be peripheral circuits capable of processing data input toor output from the first and second memory cells MC1 and MC2 (see FIG.1). For example, the peripheral circuits may include page buffers, latchcircuits, cache circuits, column decoders, sense amplifiers, data in/outcircuits, or row decoders.

For example, as illustrated in FIG. 2A, any two of the first to fourthcell blocks BF1, BF2, BF3, and BF4 may not completely overlap with eachother. As such, the driving circuit region DR provided at the fifthlevel LV5 on the substrate 110 may vertically overlap with the first tofourth cell blocks BF1, BF2, BF3, and BF4 respectively provided at thefirst to fourth levels LV1, LV2, LV3, and LV4 on the substrate 110. Anyof the first word line driving region DR_WL1, the second word linedriving region DR_WL2, the first bit line driving region DR_BL1, and thesecond bit line driving region DR_BL2 may not overlap with another.Therefore, a wiring connection structure (not shown) having a reduced orminimum length on a compact area from the first to fourth cell blocksBF1, BF2, BF3, and BF4 to the driving circuit region DR may be obtained.

In general, when cell blocks are vertically stacked in multiple layers,a wiring connection structure including bit line contacts and word linecontacts used to provide electrical connection to the cell blocks may beprovided outside the cell blocks (or provided to surround the cellblocks in a plan view). Particularly, when cell blocks are verticallystacked in multiple layers. Because a wiring connection structure forcell blocks of each layer is provided outside the cell blocks, an areaof a wiring connection region for providing the wiring connectionstructure may be increased and, thus, a total chip area of a memorydevice may also be increased.

However, according to example embodiments, the first to fourth cellblocks BF1, BF2, BF3, and BF4 may partially overlap with each other ormay be shifted or offset from each other by ½ of the first width W1 orby ½ of the second width W2. Therefore, bit line contacts and word linecontacts separately connected to the first to fourth cell blocks BF1,BF2, BF3, and BF4 may be provided on regions of the substrate 110 whichoverlap with the first to fourth cell blocks BF1, BF2, BF3, and BF4.That is, the wiring structure, according to some embodiments of theinventive concept, may be confined to an area within a polygon definedby a plan view of the first to fourth cell blocks BF1, BF2, BF3, andBF4. As such, an area of a wiring connection region may be reduced andthe memory device 10A may have a compact size.

FIG. 2B is an exploded perspective view of a memory device 10B accordingto further example embodiments of the inventive concept.

Referring to FIG. 2B, the first cell block BF1 may be provided at thefirst level LV1 and the second cell block BF2 may be provided at thesecond level LV2 on the substrate 110, and the second cell block BF2 maybe provided at a location shifted or offset from the first cell blockBF1 in a first direction (e.g., the X direction) by ½ of the first widthW1 of the first cell block BF1 in the first direction.

A driving circuit region DR, including driving circuits for separatelydriving the first and second cell blocks BF1 and BF2, may be provided atthe fifth level LV5 on the substrate 110. For example, the first wordline driving region DR_WL1, the second word line driving region DR_WL2,and the first bit line driving region DR_BL1 may be provided on thesubstrate 110. Both bit lines of the first cell block BF1 and bit linesof the second cell block BF2 may be electrically connected to the firstbit line driving region DR_BL1.

FIG. 2C is an exploded perspective view of a memory device 10C accordingto further example embodiments of the inventive concept.

Referring to FIG. 2C, the first cell block BF1 may be provided at thefirst level LV1 and the second cell block BF2 may be provided at thesecond level LV2 on the substrate 110, and the second cell block BF2 maybe provided at a location shifted or offset from the first cell blockBF1 in a second direction (e.g., the Y direction) by ½ of the secondwidth W2 of the first cell block BF1 in the second direction.

A driving circuit region DR, including driving circuits for separatelydriving the first and second cell blocks BF1 and BF2, may be provided atthe fifth level LV5 on the substrate 110. For example, the first wordline driving region DR_WL1, the first bit line driving region DR_BL1,and the second bit line driving region DR_BL2 may be provided on thesubstrate 110. Both word lines of the first cell block BF1 and wordlines of the second cell block BF2 may be electrically connected to thefirst word line driving region DR_WL1.

FIG. 3 is a perspective view of a memory device 100 according to exampleembodiments of the inventive concept. FIGS. 4 to 7 are top layout viewsof first cell blocks BF1, second cell blocks BF2, third cell blocks BF3,and fourth cell blocks BF4 of FIG. 3, respectively. FIG. 8 is across-sectional view taken along line A1-A1′ of FIGS. 4 to 7. FIG. 9 isa cross-sectional view taken along line B1-B1′ of FIGS. 4 to 7.

Referring to FIGS. 3 to 9, the memory device 100 may include a pluralityof first word lines 130-1, a plurality of second word lines 130-2, aplurality of third word lines 130-3, a plurality of first bit lines160-1, a plurality of second bit lines 160-2, and a plurality of memorycells MC provided on the substrate 110.

The first word lines 130-1 may extend on the substrate 110 in a firstdirection (e.g., the X direction of FIG. 3), and the first bit lines160-1 may extend on the first word lines 130-1 in a second direction(e.g., the Y direction of FIG. 3). The second word lines 130-2 mayextend on the first bit lines 160-1 in the first direction, the secondbit lines 160-2 may extend on the second word lines 130-2 in the seconddirection, and the third word lines 130-3 may extend on the second bitlines 160-2 in the first direction.

The memory cells MC may be provided between the first word lines 130-1and the first bit lines 160-1, between the first bit lines 160-1 and thesecond word lines 130-2, between the second word lines 130-2 and thesecond bit lines 160-2, and between the second bit lines 160-2 and thethird word lines 130-3.

The memory device 100 may include the first to fourth cell blocks BF1,BF2, BF3, and BF4 provided on the substrate 110 at different levels in athird direction (e.g., the Z direction of FIG. 3). Each first cell blockBF1 may include the first word lines 130-1 and the first bit lines160-1, and the memory cells MC therebetween, and each second cell blockBF2 may include the first bit lines 160-1 and the second word lines130-2, and the memory cells MC therebetween. Each third cell block BF3may include the second word lines 130-2 and the second bit lines 160-2,and the memory cells MC therebetween, and each fourth cell block BF4 mayinclude the second bit lines 160-2 and the third word lines 130-3, andthe memory cells MC therebetween.

FIG. 4 schematically shows the arrangement of the first word lines 130-1and the first bit lines 160-1 provided in each first cell block BF1, andfirst word line contacts 134-1 and first bit line contacts 164-1.

The first cell block BF1 may include the first word lines 130-1extending in the first direction (e.g., the X direction), and the firstbit lines 160-1 extending in the second direction (e.g., the Ydirection). The first word lines 130-1 provided in a first cell blockBF1 are not connected to the first word lines 130-1 provided in anotheradjacent first cell block BF1. The first bit lines 160-1 provided in afirst cell block BF1 are not connected to the first bit lines 160-1provided in another adjacent first cell block BF1.

As used herein, a cell block may be defined to include a plurality ofmemory cells MC configured by a first word line set including aplurality of first word lines 130-1 extending in the first direction andspaced apart from each other, and a first bit line set including aplurality of first bit lines 160-1 extending in the second direction andspaced apart from each other. That is, in FIG. 4, two first cell blocksBF1 in the first direction and two first cell blocks BF1 in the seconddirection are arranged in a matrix.

The first cell block BF1 may include first to fourth sub cell arrayregions SB1A, SB1B, SB1C, and SB1D. The first and second sub cell arrayregions SB1A and SB1B may be spaced apart from each other in the firstdirection. The third and fourth sub cell array regions SB1C and SB1D maybe spaced apart from each other in the first direction, and berespectively spaced apart from the first and second sub cell arrayregions SB1A and SB1B in the second direction. The first sub cell arrayregion SB1A may be connected to the second sub cell array region SB1B bythe first word lines 130-1, and may be connected to the third sub cellarray region SB by the first bit lines 160-1.

For example, as illustrated in FIG. 4, the first word line contacts134-1 separately connected to the first word lines 130-1 may be providedbetween the first and second sub cell array regions SB1A and SB1B. Thefirst bit line contacts 164-1 separately connected to the first bitlines 160-1 may be provided between the first and third sub cell arrayregions SB1A and SB1C.

For example, as illustrated in FIG. 4 or 8, because the first word linecontacts 134-1 are provided between the first and second sub cell arrayregions SB1A and SB1B, the first word line contacts 134-1 may overlapwith center points of the first word lines 130-1 in the first direction.That is, when each first word line 130-1 has a first length L1 (refer toFIG. 8) in the first direction, a distance between each first word linecontact 134-1 and an end of the first word line 130-1 may correspond to½ of the first length L1. Therefore, a distance between the first wordline contact 134-1 and a farthest memory cell MC therefrom maycorrespond to ½ of the first length L1.

Because the first word line contacts 134-1 are provided between thefirst and second sub cell array regions SB1A and SB1B, a distancebetween the first word line contacts 134-1 and the memory cells MC maybe reduced and the first cell block BF1 may have a lower wiringresistance. In addition, voltage drop (or IR drop) due to a resistanceof wiring lines (e.g., a resistance of the first word lines 130-1) maybe reduced and, thus, a difference or deviation in electricalcharacteristics of the memory cells MC provided in the first cell blockBF1 based on locations thereof may also be reduced.

For example, as illustrated in FIG. 5, each second cell block BF2 mayinclude first to fourth sub cell array regions SB2A, SB2B, SB2C, andSB2D. In a plan view, the second cell block BF2 may be shifted or offsetfrom the first cell block BF1 by ½ of the first width W1 (see FIG. 2A)of the first cell block BF1 in the first direction. That is, the secondword lines 130-2, provided in the second cell block BF2, may be shiftedor offset from the first word lines 130-1, provided in the first cellblock BF1, by ½ of the first width W1 in the first direction. Secondword line contacts 134-2, provided in the second cell block BF2 andconnected to the second word lines 130-2, may be spaced apart from thefirst word line contacts 134-1, provided in the first cell block BF1, by½ of the first width W1 in the first direction. Alternatively, when eachfirst word line 130-1 has the first length L1 in the first direction,the second word lines 130-2 may be shifted or offset from the first wordlines 130-1 by ½ of the first length L1 in the first direction, and thesecond word line contacts 134-2 may be spaced apart from the first wordline contacts 134-1 by ½ of the first length L1 in the first direction.That is, in a plan view, the second word line contacts 134-2 may notoverlap with the first word line contacts 134-1.

For example, as illustrated in FIGS. 6 and 7, each third cell block BF3may include first to fourth sub cell array regions SB3A, SB3B, SB3C, andSB3D. In a plan view, the third cell block BF3 may be shifted or offsetfrom the first cell block BF1 by ½ of the first width W1 of the firstcell block BF1 in the first direction, and by ½ of the second width W2of the first cell block BF1 in the second direction. Each fourth cellblock BF4 may include first to fourth sub cell array regions SB4A, SB4B,SB4C, and SB4D. In a plan view, the fourth cell block BF4 may be shiftedor offset from the first cell block BF1 by ½ of the second width W2 ofthe first cell block BF1 in the second direction.

The second bit lines 160-2, provided in the fourth cell block BF4, maybe shifted or offset from the first bit lines 160-1, provided in thefirst cell block BF1, by ½ of the second width W2 in the seconddirection. Second bit line contacts 164-2, provided in the fourth cellblock BF4 and connected to the second bit lines 160-2, may be spacedapart from the first bit line contacts 164-1, provided in the first cellblock BF1, by ½ of the second width W2 in the second direction.

In example embodiments, the third sub cell array region SB2C of thesecond cell block BF2, the first sub cell array region SB3A of the thirdcell block BF3, and the second sub cell array region SB4B of the fourthcell block BF4 may be sequentially provided on the fourth sub cell arrayregion SB1D of the first cell block BF1 in the third direction.

For example, as illustrated in FIGS. 4, 7, and 8, the third word lines130-3 provided in the fourth cell block BF4 may vertically overlap withthe first word lines 130-1 provided in the first cell block BF1. Thirdword line contacts 134-3 separately connected to the third word lines130-3 may overlap with the first word line contacts 134-1 separatelyconnected to the first word lines 130-1. The third word lines 130-3 maybe separately and electrically connected to the first word lines 130-1by the third word line contacts 134-3. As such, the third word lines130-3 may be electrically connected to the first word line drivingregion DR_WL1 for driving the first word lines 130-1 through the thirdword line contacts 134-3 and the first word line contacts 134-1.

For example, as illustrated in FIG. 8, the first word line drivingregion DR_WL1 may vertically overlap with the first word line contacts134-1 of the first cell block BF1 and the third word line contacts 134-3of the fourth cell block BF4, but embodiments of the inventive conceptare not limited thereto. The second word line driving region DR_WL2 mayvertically overlap with the second word line contacts 134-2 of thesecond and third cell blocks BL2 and BL3. The first bit line drivingregion DR_BL1 may vertically overlap with the first bit line contacts164-1 of the first and second cell blocks BF1 and BF2, and the secondbit line driving region DR_BL2 may vertically overlap with the secondbit line contacts 164-2 of the third and fourth cell blocks BF3 and BF4.

As illustrated in FIGS. 8 and 9, a plurality of transistors TR forconfiguring driving circuits may be provided on the substrate 110. Anactive region (not shown) for the driving circuits may be defined on thesubstrate 110 by an isolation layer 112, and the transistors TR may beprovided on the active region. Each of the transistors TR may include agate GL, a gate insulating layer GI, and source/drain regions SD. Bothside walls of the gate GL may be covered with a gate spacer GS, and anetch stop layer 114 may be provided on a top surface 110T of thesubstrate 110 to cover the gate GL and the gate spacer GS. The etch stoplayer 114 may include an insulating material, such as silicon nitride orsilicon oxynitride.

An interlayer insulating layer 120 may be provided on the etch stoplayer 114, the interlayer insulating layer 120 including a first lowerinsulating layer 120-1, a second lower insulating layer 120-2, a thirdlower insulating layer 120-3, and a fourth lower insulating layer 120-4.A multilayer wiring structure 124 may be electrically connected to eachof the transistors TR. The multilayer wiring structure 124 may include afirst via 126-1, a first wiring layer 128-1, a second via 126-2, and asecond wiring layer 128-2, which are sequentially stacked on one anotherand electrically connected to each other on the substrate 110, and maybe surrounded by the interlayer insulating layer 120. The interlayerinsulating layer 120 may be made of an oxide, such as silicon oxide, ora nitride, such as silicon nitride.

Each of the first word lines 130-1, the first bit lines 160-1, thesecond word lines 130-2, the second bit lines 160-2, and the third wordlines 130-3 may be made of a metal, a conductive metal nitride, aconductive metal oxide, or a combination thereof. For example, each ofthe first word lines 130-1, the first bit lines 160-1, the second wordlines 130-2, the second bit lines 160-2, and the third word lines 130-3may be made of tungsten (W), tungsten nitride (WN), gold (Au), silver(Ag), copper (Cu), aluminum (Al), titanium aluminum nitride (TiAlN),iridium (Ir), platinum (Pt), palladium (Pd), ruthenium (Ru), zirconium(Zr), rhodium (Rh), nickel (Ni), cobalt (Co), chromium (Cr), tin (Sn),zinc (Zn), indium tin oxide (ITO), an alloy thereof, or a combinationthereof, or include a metal layer and a conductive barrier layercovering at least a part of the metal layer. The conductive barrierlayer may be made of, for example, titanium (Ti), titanium nitride(TiN), tantalum (Ta), tantalum nitride (TaN), or a combination thereof.

The memory cells MC may be provided between the first word lines 130-1,the first bit lines 160-1, the second word lines 130-2, the second bitlines 160-2, and the third word lines 130-3. Each memory cell MC mayinclude a switching unit 140 and a memory unit 150 provided on theswitching unit 140. In example embodiments, the memory cells MC may havea rectangular pillar shape. In other embodiments, the memory cells MCmay have various pillar shapes, such as, but not limited to, circular,oval, or polygonal pillar shapes.

A first insulating layer 132-1 may be provided on the interlayerinsulating layer 120 between the first word lines 130-1, and a secondinsulating layer 148-1 may be provided on the first insulating layer132-1 and the first word lines 130-1 to fill spaces between adjacentones of the memory cells MC. A third insulating layer 162-1 may beprovided on the second insulating layer 148-1 between adjacent ones ofthe first bit lines 160-1, and a fourth insulating layer 148-2 may beprovided on the third insulating layer 162-1 and the first bit lines160-1 to fill spaces between adjacent ones of the memory cells MC. Afifth insulating layer 132-2 may be provided on the fourth insulatinglayer 148-2 between adjacent ones of the second word lines 130-2, and asixth insulating layer 148-3 may be provided on the fifth insulatinglayer 132-2 and the second word lines 130-2 to fill spaces betweenadjacent ones of the memory cells MC. A seventh insulating layer 162-2may be provided on the sixth insulating layer 148-3 between adjacentones of the second bit lines 160-2, and an eighth insulating layer 148-4may be provided on the seventh insulating layer 162-2 and the second bitlines 160-2 to fill spaces between adjacent ones of the memory cells MC.A ninth insulating layer 132-3 may be provided on the eighth insulatinglayer 148-4 between adjacent ones of the third word lines 130-3.Meanwhile, the first to ninth insulating layers 132-1, 148-1, 162-1,148-2, 132-2, 148-3, 162-2, 148-4, and 132-3 may be made of the samematerial, or, in other embodiments, at least one thereof may be made ofa different material from the others. For example, the first to ninthinsulating layers 132-1, 148-1, 162-1, 148-2, 132-2, 148-3, 162-2,148-4, and 132-3 may include one or more of silicon oxide, siliconnitride, or silicon oxynitride. Air spaces (not shown) may be providedinstead of at least one of the first to ninth insulating layers 132-1,148-1, 162-1, 148-2, 132-2, 148-3, 162-2, 148-4, and 132-3 and, in thisembodiment, an insulating liner (not shown) having a certain thicknessmay be provided between the air spaces and the memory cells MC.

For example, as illustrated in FIGS. 8 and 9, the first word linecontacts 134-1 may pass through the interlayer insulating layer 120 andbe electrically connected to the first word line driving region DR_WL1provided on the substrate 110. The second word line contacts 134-2 maypass through the interlayer insulating layer 120 and the first to fourthinsulating layers 132-1, 148-1, 162-1, and 148-2 and be electricallyconnected to the second word line driving region DR_WL2. The first bitline contacts 164-1 may pass through the interlayer insulating layer 120and the first and second insulating layers 132-1 and 148-1 and beelectrically connected to the first bit line driving region DR_BL1, andthe second bit line contacts 164-2 may pass through the interlayerinsulating layer 120 and the first to sixth insulating layers 132-1,148-1, 162-1, 148-2, 132-2, and 148-3 and be electrically connected tothe second bit line driving region DR_BL2. The third word line contacts134-3 may be electrically connected to the first word line drivingregion DR_WL1 through the first word line contacts 134-1.

In general, when cell blocks are vertically stacked in multiple layers,a wiring connection structure including bit line contacts and word linecontacts used to provide electrical connection to the cell blocks may beprovided outside the cell blocks. Particularly, when cell blocks arevertically stacked in multiple layers, because a wiring connectionstructure for cell blocks of each layer is provided outside the cellblocks, an area of a wiring connection region for providing the wiringconnection structure may be increased and, thus, a total chip area of amemory device may also be increased.

However, according to the afore-described example embodiments, the firstthrough third word line contacts 134-1, 134-2, and 134-3 and the firstand second bit line contacts 164-1 and 164-2 may be provided atlocations overlapping with the first to fourth cell blocks BF1, BF2,BF3, and BF4. Therefore, a wiring connection structure having a reducedor minimum length from the first to fourth cell blocks BF1, BF2, BF3,and BF4 to the driving circuit region DR (see FIG. 2A) may be obtainedby the first through third word line contacts 134-1, 134-2, and 134-3and the first and second bit line contacts 164-1 and 164-2. Thus, thememory device 100 may have a relatively compact size.

In addition, according to the afore-described example embodiments,because the first word line contacts 134-1 are provided between thefirst and second sub cell array regions SB1A and SB1B, a distancebetween the first word line contacts 134-1 and the memory cells MC maybe reduced, and, thus, voltage drop (or IR drop) due to a resistance ofwiring lines may also be reduced. Consequently, a difference ordeviation in electrical characteristics of the memory cells MC providedin the first to fourth cell blocks BF1, BF2, BF3, and BF4 based onlocations thereof may be reduced.

Detailed configurations of memory cells MC, MC-1, MC-2, MC-3, and MC-4according to example embodiments of the inventive concept will now bedescribed with reference to FIGS. 10 to 14.

Referring to FIG. 10, the memory cell MC may include the switching unit140 and the memory unit 150 provided on the switching unit 140. Theswitching unit 140 may include a first electrode layer 142, a switchingmaterial layer 144, and a second electrode layer 146 sequentiallystacked on each of a plurality of first word lines 130-1.

The switching material layer 144 may be a current control layerconfigured to control the flow of a current. The switching materiallayer 144 may include a material layer, a resistance of which isvariable based on the magnitude of a voltage applied to both ends of theswitching material layer 144 and/or a current passing therethrough. Forexample, the switching material layer 144 may include a material layerhaving Ovonic threshold switching (OTS) characteristics. Examplefunctionality of the switching material layer 144 based on the OTSmaterial layer will now be briefly described. When a voltage lower thana threshold voltage is applied to the switching material layer 144, theswitching material layer 144 is maintained in a high-resistance stateand, thus, little current flows therethrough. When a voltage higher thanthe threshold voltage is applied to the switching material layer 144,the switching material layer 144 is in a low-resistance state and, thus,a current starts to flow therethrough. When the current flowing throughthe switching material layer 144 is lower than a holding current, theswitching material layer 144 may transition to a high-resistance state.

The switching material layer 144 may include a chalcogenide material asthe OTS material layer. In example embodiments, the switching materiallayer 144 may include silicon (Si), tellurium (Te), arsenic (As),germanium (Ge), indium (In), or a combination thereof. For example, theswitching material layer 144 may include silicon (Si) at a content ofabout 14%, tellurium (Te) at a content of about 39%, arsenic (As) at acontent of about 37%, germanium (Ge) at a content of about 9%, andindium (In) at a content of about 1%. Herein, the percentages are atomicpercentages out of a total of 100%, and this principle may be equallyapplied to the following description. In other embodiments, theswitching material layer 144 may include silicon (Si), tellurium (Te),arsenic (As), germanium (Ge), sulfur (S), selenium (Se), or acombination thereof. For example, the switching material layer 144 mayinclude silicon (Si) at a content of about 5%, tellurium (Te) at acontent of about 34%, arsenic (As) at a content of about 28%, germanium(Ge) at a content of about 11%, sulfur (S) at a content of about 21%,and selenium (Se) at a content of about 1%. In other embodiments, theswitching material layer 144 may include silicon (Si), tellurium (Te),arsenic (As), germanium (Ge), sulfur (S), selenium (Se), antimony (Sb),or a combination thereof. For example, the switching material layer 144may include tellurium (Te) at a content of about 21%, arsenic (As) at acontent of about 10%, germanium (Ge) at a content of about 15%, sulfur(S) at a content of about 2%, selenium (Se) at a content of about 50%,and antimony (Sb) at a content of about 2%.

The switching material layer 144 is not limited to the OTS materiallayer, and may include various material layers operable to select adevice. For example, the switching material layer 144 may include, butis not limited to, a diode, a tunnel junction, a PNP diode or a bipolarjunction transistor (BJT), a mixed ionic-electronic conduction (MIEC)material, or the like.

The first and second electrode layers 142 and 146 may serve as a currentpath and be made of a conductive material. For example, each of thefirst and second electrode layers 142 and 146 may be made of a metal, aconductive metal nitride, a conductive metal oxide, or a combinationthereof. Each of the first and second electrode layers 142 and 146 mayinclude a titanium nitride (TiN) layer, but embodiments of the inventiveconcept are not limited thereto.

The memory unit 150 may include a third electrode layer 152, a variableresistance layer 154, and a fourth electrode layer 156 sequentiallystacked on the switching unit 140.

In example embodiments, the variable resistance layer 154 may include aphase change material, which is reversibly changed between an amorphousstate and a crystalline state based on a heating time. For example, thevariable resistance layer 154 may have a phase which is reversiblychangeable by Joule heat generated due to a voltage applied to both endsof the variable resistance layer 154, and may include a material, aresistance of which is variable due to the phase change. Specifically,the phase change material may transition to a high-resistance state inan amorphous phase, and transition to a low-resistance state in acrystalline phase. By defining the high-resistance state as “0” anddefining the low-resistance state as “1,” data may be stored in thevariable resistance layer 154.

In some embodiments, the variable resistance layer 154 may include oneor more elements (chalcogen elements) from group VI in the periodictable, and may include one or more chemical modifiers from group III,IV, or V in the periodic table. For example, the variable resistancelayer 154 may include Ge—Sb—Te. Herein, the chemical composition usinghyphens may indicate elements included in a certain mixture or compound,and represent all chemical structures including the indicated elements.For example, Ge—Sb—Te may be a material compound, such as Ge₂Sb₂Te₅,Ge₂Sb₂Te₇, Ge₁Sb₂Te₄, or Ge₁Sb₄Te₇.

In addition to Ge—Sb—Te, the variable resistance layer 154 may includevarious phase change materials. For example, the variable resistancelayer 154 may include at least one or a combination of Ge—Te, Sb—Te,In—Se, Ga—Sb, In—Sb, As—Te, Al—Te, Bi—Sb—Te (BST), In—Sb—Te (IST),Ge—Sb—Te, Te—Ge—As, Te—Sn—Se, Ge—Se—Ga, Bi—Se—Sb, Ga—Se—Te, Sn—Sb—Te,In—Sb—Ge, In—Ge—Te, Ge—Sn—Te, Ge—Bi—Te, Ge—Te—Se, As—Sb—Te, Sn—Sb—Bi,Ge—Te—O, Te—Ge—Sb—S, Te—Ge—Sn—O, Te—Ge—Sn—Au, Pd—Te—Ge—Sn, In—Se—Ti—Co,Ge—Sb—Te—Pd, Ge—Sb—Te—Co, Sb—Te—Bi—Se, Ag—In—Sb—Te, Ge—Sb—Se—Te,Ge—Sn—Sb—Te, Ge—Te—Sn—Ni, Ge—Te—Sn—Pd, Ge—Te—Sn—Pt, In—Sn—Sb—Te, andAs—Ge—Sb—Te.

Each element of the variable resistance layer 154 may have variousstoichiometric ratios. Crystallization temperature, melting temperature,phase change speed based on crystallization energy, and data retentioncharacteristics of the variable resistance layer 154 may be controlledbased on the stoichiometric ratio of each element.

The variable resistance layer 154 may further include at least oneimpurity among carbon (C), nitrogen (N), silicon (Si), oxygen (O),bismuth (Bi), and tin (Sn). A driving current of the memory device 100may be changed by the impurity. The variable resistance layer 154 mayfurther include a metal. For example, the variable resistance layer 154may include at least one of aluminum (Al), gallium (Ga), zinc (Zn),titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co),nickel (Ni), molybdenum (Mo), ruthenium (Ru), palladium (Pd), hafnium(Hf), tantalum (Ta), iridium (Ir), platinum (Pt), zirconium (Zr),thallium (Tl), lead (Pb), and polonium (Po). The above-mentionedmetallic materials may increase electrical conductivity and thermalconductivity of the variable resistance layer 154, thereby increasingcrystallization speed and set speed. In addition, the metallic materialsmay improve data retention characteristics of the variable resistancelayer 154.

The variable resistance layer 154 may have a multilayer structure inwhich two or more layers having different properties are stacked on oneanother. The number or thickness of the layers may be freely selected. Abarrier layer configured to reduce or prevent diffusion of a materialbetween the layers may be further provided between the layers. Inaddition, the variable resistance layer 154 may have a super-latticestructure in which a plurality of layers including different materialsare alternately stacked on one another. For example, the variableresistance layer 154 may have a structure in which first layers made ofGe—Te and second layers made of Sb—Te are alternately stacked on oneanother. However, the first and second layers are not limited to Ge—Teand Sb—Te, and may include the above-mentioned various materials.

Although the variable resistance layer 154 includes a phase changematerial in the embodiments described above, embodiments of theinventive concept are not limited thereto and the variable resistancelayer 154 may include various materials having variable resistancecharacteristics in other embodiments.

In some embodiments, when the variable resistance layer 154 includes atransition metal oxide, the memory device 100 may be resistive RAM(ReRAM). Using the variable resistance layer 154 including a transitionmetal oxide, at least one electrical path may be generated in oreliminated from the variable resistance layer 154 due to a programoperation. The variable resistance layer 154 may have a low resistancevalue when the electrical path is generated, and have a high resistancevalue when the electrical path is eliminated. The memory device 100 maystore data by using the difference in the resistance value of thevariable resistance layer 154.

When the variable resistance layer 154 is made of a transition metaloxide, the transition metal oxide may include at least one metalselected among tantalum (Ta), zirconium (Zr), titanium (Ti), hafnium(Hf), manganese (Mn), yttrium (Y), nickel (Ni), cobalt (Co), zinc (Zn),niobium (Nb), copper (Cu), iron (Fe), and chromium (Cr). For example,the transition metal oxide may include a monolayer or a multilayer madeof at least one material selected among Ta₂O_(5-x), ZrO_(2-x),TiO_(2-x), HfO_(2-x), MnO_(2-x), Y₂O_(3-x), Nb₂O_(5-x), CuO_(1-y), andFe₂O_(3-x). In the above-mentioned materials, x and y may be selected inranges of 0≤x≤1.5 and 0≤y≤0.5, but embodiments of the inventive conceptare not limited thereto.

In other embodiments, when the variable resistance layer 154 has amagnetic tunnel junction (MTJ) structure including two electrodes madeof a magnetic material, and a dielectric provided between the twomagnetic electrodes, the memory device 100 may be magnetic RAM (MRAM).

The two electrodes may be a pinned layer (or a fixed layer) and a freelayer, and the dielectric provided between the two electrodes may be atunnel barrier layer. The pinned layer may have a magnetizationdirection, which is pinned to a direction, and the free layer may have amagnetization direction, which is changeable to be parallel orantiparallel to the magnetization direction of the pinned layer. Themagnetization directions of the pinned layer and the free layer may beparallel to a surface of the tunnel barrier layer, but embodiments ofthe inventive concept are not limited thereto. The magnetizationdirections of the pinned layer and the free layer may be perpendicularto a surface of the tunnel barrier layer.

When the magnetization direction of the free layer is parallel to themagnetization direction of the pinned layer, the variable resistancelayer 154 may have a first resistance value. When the magnetizationdirection of the free layer is antiparallel to the magnetizationdirection of the pinned layer, the variable resistance layer 154 mayhave a second resistance value. The memory device 100 may store data byusing the difference in the resistance value. The magnetizationdirection of the free layer may be changed due to spin torque ofelectrons in a program current.

The pinned layer and the free layer may include a magnetic material. Inthese embodiments, the pinned layer may further include anantiferromagnetic material for pinning a magnetization direction of theferromagnetic material in the pinned layer. The tunnel barrier layer maybe made of an oxide of any one material selected among Mg, Ti, Al, MgZn,and MgB, but embodiments of the inventive concept are not limited to theabove-mentioned materials.

The third and fourth electrode layers 152 and 156 may serve as a currentpath and may be made of a conductive material. For example, each of thethird and fourth electrode layers 152 and 156 may be made of a metal, aconductive metal nitride, a conductive metal oxide, or a combinationthereof. In example embodiments, at least one of the third and fourthelectrode layers 152 and 156 may include a conductive materialconfigured to generate sufficient heat to change the phase of thevariable resistance layer 154. For example, the third and fourthelectrode layers 152 and 156 may be made of a high-melting-point metal,such as TiN, TiSiN, TiAlN, TaSiN, TaAlN, TaN, WSi, WN, TiW, MoN, NbN,TiBN, ZrSiN, WSiN, WBN, ZrAlN, MoAlN, TiAl, TiON, TiAlON, WON, TaON, C,SiC, SiCN, CN, TiCN, TaCN, or a combination thereof, a nitride thereof,or a carbon-based conductive material. However, embodiments of the thirdand fourth electrode layers 152 and 156 are not limited to theabove-mentioned materials. In other embodiments, each of the third andfourth electrode layers 152 and 156 may include a conductive layer madeof a metal, a conductive metal nitride, or a conductive metal oxide, andat least one conductive barrier layer covering at least a part of theconductive layer. The conductive barrier layer may be made of a metaloxide, a metal nitride, or a combination thereof, but embodiments of theinventive concept are not limited thereto.

In other embodiments, at least one of the first to fourth electrodelayers 142, 146, 152, and 156 may be omitted. One of the second andthird electrode layers 146 and 152 may not be omitted to reduce orprevent contamination or contact failure due to direct contact betweenthe switching material layer 144 and the variable resistance layer 154.In addition, any one of the second and third electrode layers 146 and152 may have a larger thickness than the other. As such, when the thirdor fourth electrode layer 152 or 156 is heated to change the phase ofthe variable resistance layer 154, influence of the heat on theswitching material layer 144 adjacent thereto may be reduced orprevented (for example, deterioration or damage, e.g., partialcrystallization, of the switching material layer 144 due to the heatprovided from the third or fourth electrode layer 152 or 156 may bereduced or prevented).

Referring to FIG. 11, the memory cell MC-1 may include the memory unit150 provided on the first word lines 130-1, and the switching unit 140provided on the memory unit 150.

According to example embodiments, the memory cell MC-1 may be used inthe memory device 100 together with the memory cell MC described abovewith respect to FIG. 10. For example, to achieve approximately equaldirections of currents flowing through the memory cells MC and MC-1, thememory cell MC-1 may be provided between the first word lines 130-1 andthe first bit lines 160-1, and the memory cell MC may be providedbetween the first bit lines 160-1 and the second word lines 130-2.

Referring to FIG. 12, the memory cell MC-2 may have sloping side walls150SW, and a width of a top surface of the variable resistance layer 154in a second direction (e.g., the Y direction) may be less than a widthof a top surface of the switching material layer 144 in the seconddirection.

In example embodiments, the memory cell MC-2 may be produced by forminga memory stack (not shown) on the first word lines 130-1 and the firstinsulating layer 132-1, forming a mask pattern (not shown) on the memorystack, and then performing an anisotropic etching process on the memorystack by using the mask pattern as an etching mask. An upper part of thememory cell MC-2 may be exposed to an etching atmosphere for a longertime in the anisotropic etching process, and, thus, the memory cell MC-2may have the sloping side walls 150SW.

Referring to FIG. 13, the memory cell MC-3 may further include a spacer158 provided on both side walls of the variable resistance layer 154.

In example embodiments, an insulating layer (not shown) may be formed onthe third electrode layer 152, a trench may be formed in the insulatinglayer, and then the spacer 158 may be formed on side walls of thetrench. Thereafter, the variable resistance layer 154 may be formed onthe spacer 158 to fill the trench. A width of a lower part of the spacer158 may be greater than that of an upper part thereof. Theabove-described process may also be referred to as a damascene process.

Referring to FIG. 14, the memory cell MC-4 may include a third electrodelayer 152A having an ‘L’ shape, and a spacer 152B may be provided onboth side walls of the third electrode layer 152A.

The third electrode layer 152A may include a conductive materialconfigured to generate sufficient heat to change the phase of thevariable resistance layer 154. Herein, the third electrode layer 152Amay be referred to as a heating electrode. Reliability of the memoryunit 150 may be increased due to a small contact area between the thirdelectrode layer 152A and the variable resistance layer 154.

FIG. 15 is a top layout view of a memory device 100A according toexample embodiments of the inventive concept. FIG. 15 shows the layoutof the fourth cell blocks BF4 of FIG. 3. In FIGS. 1 to 15, likereference numerals denote like elements.

Referring to FIG. 15, third word line contacts 134-3A and 134-3B may bearranged in a zigzag form. That is, the third word line contacts 134-3Aconnected to odd-numbered third word lines 130-3 may be spaced apartfrom the third word line contacts 134-3B connected to even-numberedthird word lines 130-3, by a certain distance in a first direction(e.g., the X direction).

Although not shown in FIG. 15, all of the first word line contacts134-1, the second word line contacts 134-2, the first bit line contacts164-1, and the second bit line contacts 164-2 may be arranged in azigzag form, similar to the third word line contacts 134-3A and 134-3B.

FIG. 16 is a cross-sectional view of a memory device 100B according toexample embodiments of the inventive concept. FIG. 16 shows across-section corresponding to the cross-sectional view taken along lineB1-B1′ of FIGS. 4 to 7. In FIGS. 1 to 16, like reference numerals denotelike elements.

Referring to FIG. 16, each of the first and second bit line contacts164-1 and 164-2 may include a plurality of studs CO U. For example, thefirst bit line contact 164-1 may have a stacked structure of a stud COUsurrounded by the interlayer insulating layer 120 and a stud CO Usurrounded by the first and second insulating layers 132-1 and 148-1.The second bit line contact 164-2 may have a stacked structure of a studCOU surrounded by the interlayer insulating layer 120, a stud COUsurrounded by the first and second insulating layers 132-1 and 148-1, astud COU surrounded by the third and fourth insulating layers 162-1 and148-2, and a stud COU surrounded by the fifth and sixth insulatinglayers 132-2 and 148-3.

Although not shown in FIG. 16, the first word line contacts 134-1 (seeFIG. 8), the second word line contacts 134-2 (see FIG. 8), and the thirdword line contacts 134-3 (see FIG. 8) may also have a stacked structureof a plurality of studs CO U.

FIGS. 17 and 18 are cross-sectional views of a memory device 100Caccording to example embodiments of the inventive concept. FIG. 17 showsa cross-section corresponding to the cross-sectional view taken alongline A1-A1′ of FIGS. 4 to 7, and FIG. 18 shows a cross-sectioncorresponding to the cross-sectional view taken along line B1-B1′ ofFIGS. 4 to 7. In FIGS. 1 to 18, like reference numerals denote likeelements.

Referring to FIGS. 17 and 18, a plurality of first word lines 130-1, aplurality of second word lines 130-2, a plurality of third word lines130-3, and a plurality of fourth word lines 130-4, which extend in afirst direction (e.g., the X direction), and a plurality of first bitlines 160-1, a plurality of second bit lines 160-2, a plurality of thirdbit lines 160-3, and a plurality of fourth bit lines 160-4, which extendin a second direction (e.g., the Y direction), may be provided on thesubstrate 110 at different levels.

The memory cells MC may be provided between the first word lines 130-1and the first bit lines 160-1, between the second word lines 130-2 andthe second bit lines 160-2, between the third word lines 130-3 and thethird bit lines 160-3, and between the fourth word lines 130-4 and thefourth bit lines 160-4.

The first word lines 130-1 may vertically overlap with the fourth wordlines 130-4, and first word line contacts 134-1 separately connected tothe first word lines 130-1 may be electrically connected to fourth wordline contacts 134-4, which are separately connected to the fourth wordlines 130-4. The second word lines 130-2 may vertically overlap with thethird word lines 130-3, and second word line contacts 134-2 separatelyconnected to the second word lines 130-2 may be electrically connectedto third word line contacts 134-3, which are separately connected to thethird word lines 130-3.

The first bit lines 160-1 may vertically overlap with the second bitlines 160-2, and first bit line contacts 164-1 separately connected tothe first bit lines 160-1 may be electrically connected to second bitline contacts 164-2, which are separately connected to the second bitlines 160-2. The third bit lines 160-3 may vertically overlap with thefourth bit lines 160-4, and third bit line contacts 164-3 separatelyconnected to the third bit lines 160-3 may be electrically connected tofourth bit line contacts 164-4, which are separately connected to thefourth bit lines 160-4.

Interlayer insulating layers 182-1, 182-2, and 182-3 may be furtherprovided between the first bit lines 160-1 and the second word lines130-2, between the second bit lines 160-2 and the third word lines130-3, and between the third bit lines 160-3 and the fourth word lines130-4.

FIGS. 19 and 20 are cross-sectional views of a memory device 100Daccording to further example embodiments of the inventive concept. FIG.19 shows a cross-section corresponding to the cross-sectional view takenalong line A1-A1′ of FIGS. 4 and 5, and FIG. 20 shows a cross-sectioncorresponding to the cross-sectional view taken along line B1-B1′ ofFIGS. 4 and 5.

Referring to FIGS. 19 and 20, the first word lines 130-1 may extend onthe substrate 110 in a first direction (e.g., the X direction of FIG.19), and the first bit lines 160-1 may extend on the first word lines130-1 in a second direction (e.g., the Y direction of FIG. 20). Thesecond word lines 130-2 may extend on the first bit lines 160-1 in thefirst direction, and be shifted or offset from the first word lines130-1 in the first direction by ½ of the first width W1 (see FIG. 2B).The second bit lines 160-2 may extend on the second word lines 130-2 inthe second direction, and vertically overlap with the first bit lines160-1.

The second bit lines 160-2 may be separately and electrically connectedto the first bit lines 160-1 through the second bit line contacts 164-2,and the first bit lines 160-1 may be separately and electricallyconnected to the first bit line driving region DR_BL1 through the firstbit line contacts 164-1.

According to the afore-described example embodiments, because the firstand second word line contacts 134-1 and 134-2 and the first and secondbit line contacts 164-1 and 164-2 are connected to center points of thefirst and second word lines 130-1 and 130-2 and the first and second bitlines 160-1 and 160-2, a wiring connection structure having a reduced orminimum length from the first and second word lines 130-1 and 130-2 andthe first and second bit lines 160-1 and 160-2 to the driving circuitregion DR (see FIG. 2B) may be obtained. Therefore, the memory device100D may have a relatively compact size. In addition, because the firstand second word line contacts 134-1 and 134-2 and the first and secondbit line contacts 164-1 and 164-2 are connected to center points of thefirst and second word lines 130-1 and 130-2 and the first and second bitlines 160-1 and 160-2, a difference or deviation in electricalcharacteristics of the memory cells MC based on locations thereof may bereduced.

FIGS. 21 and 22 are cross-sectional views of a memory device 100Eaccording to further example embodiments of the inventive concept. FIG.21 shows a cross-section corresponding to the cross-sectional view takenalong line A1-A1′ of FIGS. 4 and 5, and FIG. 22 shows a cross-sectioncorresponding to the cross-sectional view taken along line B1-B1′ ofFIGS. 4 and 5.

Referring to FIGS. 21 and 22, the first word lines 130-1 may extend onthe substrate 110 in a first direction (e.g., the X direction of FIG.21), and the first bit lines 160-1 may extend on the first word lines130-1 in a second direction (e.g., the Y direction of FIG. 22). Thesecond word lines 130-2 may extend on the first bit lines 160-1 in thefirst direction, and vertically overlap with the first word lines 130-1.The second bit lines 160-2 may extend on the second word lines 130-2 inthe second direction, and be shifted or offset from the first bit lines160-1 in the second direction by ½ of the second width W2 (see FIG. 2C).

The second word lines 130-2 may be separately and electrically connectedto the first word lines 130-1 through the second word line contacts134-2, and the first word lines 130-1 may be separately and electricallyconnected to the first word line driving region DR_WL1 through the firstword line contacts 134-1.

According to the afore-described example embodiments, because the firstand second word line contacts 134-1 and 134-2 and the first and secondbit line contacts 164-1 and 164-2 are connected to center points of thefirst and second word lines 130-1 and 130-2 and the first and second bitlines 160-1 and 160-2, a wiring connection structure having a reduced orminimum length from the first and second word lines 130-1 and 130-2 andthe first and second bit lines 160-1 and 160-2 to the driving circuitregion DR (see FIG. 2C) may be obtained. Therefore, the memory device100E may have a relatively compact size. In addition, because the firstand second word line contacts 134-1 and 134-2 and the first and secondbit line contacts 164-1 and 164-2 are connected to center points of thefirst and second word lines 130-1 and 130-2 and the first and second bitlines 160-1 and 160-2, a difference or deviation in electricalcharacteristics of the memory cells MC based on locations thereof may bereduced.

While the inventive concept has been particularly shown and describedwith reference to embodiments thereof, it will be understood thatvarious changes in form and details may be made therein withoutdeparting from the spirit and scope of the following claims.

What is claimed is:
 1. A memory device comprising: a first word line ona substrate at a first level, the first word line extending in a firstdirection parallel to a top surface of the substrate, the first wordline having a first length in the first direction; a second word line onthe substrate at a second level higher than the first level, the secondword line extending in the first direction, the second word line beingshifted from the first word line in the first direction by about ½ ofthe first length; a third word line on the substrate at a third levelhigher than the second level, the third word line extending in the firstdirection, the third word line vertically overlapping the second wordline; a fourth word line on the substrate at a fourth level higher thanthe third level, the fourth word line extending in the first direction,the fourth word line vertically overlapping the first word line; and aplurality of memory cells, each of the plurality of memory cells beingdisposed on the first through fourth word lines.
 2. The memory device ofclaim 1, further comprising: a first bit line on the first word linesuch that a first memory cell among the plurality of memory cells isdisposed between the first word line and the first bit line, the firstbit line extending in a second direction that is parallel to the topsurface of the substrate and intersecting the first direction; a secondbit line on the second word line such that a second memory cell amongthe plurality of memory cells is disposed between the second word lineand the second bit line, the second bit line extending in the seconddirection; a third bit line on the third word line such that a thirdmemory cell among the plurality of memory cells is disposed between thethird word line and the third bit line, the third bit line extending inthe second direction; and a fourth bit line on the fourth word line suchthat a fourth memory cell among the plurality of memory cells isdisposed between the fourth word line and the fourth bit line, thefourth bit line extending in the second direction.
 3. The memory deviceof claim 2, wherein the first bit line has a second length in the seconddirection, and the second bit line is shifted from the first bit line inthe second direction by about ½ of the second length.
 4. The memorydevice of claim 2, further comprising: a first cell block including thefirst word line, the first bit line, and the first memory cell; a secondcell block including the second word line, the second bit line, and thesecond memory cell; a third cell block including the third word line,the third bit line, and the third memory cell; a fourth cell blockincluding the fourth word line, the fourth bit line, and the fourthmemory cell, wherein the second cell block is shifted from the firstcell block in the first direction by about ½ of the first length.
 5. Thememory device of claim 1, further comprising: a first word line contactconnected to a bottom surface of the first word line; a second word linecontact connected to a bottom surface of the second word line, thesecond word line contact being shifted from the first word line contactin the first direction by about ½ of the first length; a third word linecontact connected to a bottom surface of the third word line, the thirdword line contact vertically overlapping the second word line contact;and a fourth word line contact connected to a bottom surface of thefourth word line, the fourth word line contact vertically overlappingthe first word line contact.
 6. The memory device of claim 5, whereinthe third word line contact is connected to a top surface of the secondword line, and the fourth word line contact is connected to a topsurface of the first word line.
 7. The memory device of claim 5, whereinthe first word line contact is disposed under a center point of thebottom surface of the first word line, and the fourth word line contactis disposed on a center point of a top surface of the first word line.8. The memory device of claim 5, further comprising: a first word linedriving region on the substrate, the first word line driving regionbeing at a level lower that the first level; and a second word linedriving region on the substrate, the second word line driving regionbeing at a level lower that the first level, wherein the first word linecontact connects the first word line to the first word line drivingregion, and the second word line contact connects the second word lineto the second word line driving region.
 9. The memory device of claim 5,wherein the first word line contact includes a plurality of studsstacked in a third direction perpendicular to the top surface of thesubstrate, and the second word line contact includes a plurality ofstuds stacked in the third direction.
 10. The memory device of claim 1,wherein each of the plurality of memory cells includes a memory unit anda switching unit, the memory unit and the switching unit is arranged ina third direction perpendicular to the top surface of the substrate, andthe switching unit includes an Ovonic threshold switching (OTS) device.11. The memory device of claim 10, wherein each of the plurality ofmemory cells includes an inclined sidewall, a top surface of each of theplurality of memory cells has a first width in the first direction, abottom surface of each of the plurality of memory cells has a secondwidth in the first direction, and the second width is greater than thefirst width.
 12. A memory device comprising: a first word line on asubstrate at a first level, the first word line extending in a firstdirection parallel to a top surface of the substrate, the first wordline having a first length in the first direction; a second word line onthe substrate at a second level higher than the first level, the secondword line extending in the first direction, the second word line beingshifted from the first word line in the first direction by about ½ ofthe first length; a third word line on the substrate at a third levelhigher than the second level, the third word line extending in the firstdirection, the third word line vertically overlapping the second wordline; a first bit line between the first word line and the second wordline, the first bit line extending in a second direction that isparallel to the top surface of the substrate and intersecting the firstdirection; and a second bit line between the second word line and thethird word line, the second bit line extending in the second direction.13. The memory device of claim 12, further comprising: a first word linecontact connected to a bottom surface of the first word line; a secondword line contact connected to a bottom surface of the second word line,the second word line contact being shifted from the first word linecontact in the first direction by about ½ of the first length; and athird word line contact connected to a bottom surface of the third wordline, the third word line contact vertically overlapping the first wordline contact.
 14. The memory device of claim 13, wherein each of thefirst through third word line contacts includes a plurality of studsstacked in a third direction perpendicular to the top surface of thesubstrate.
 15. The memory device of claim 12, wherein the first bit linehas a second length in the second direction, and the second bit line isshifted from the first bit line in the second direction by about ½ ofthe second length.
 16. The memory device of claim 15, furthercomprising: a first bit line contact connected to a bottom surface ofthe first bit line; and a second bit line contact connected to a bottomsurface of the second bit line, the second bit line contact beingshifted from the first bit line contact in the second direction by about½ of the second length.
 17. The memory device of claim 12, furthercomprising: a first cell block including the first word line, the firstbit line, and a first memory cell between the first word line and thefirst bit line; a second cell block including the first bit line, thesecond word line, and a second memory cell between the first bit lineand the second word line; a third cell block including the second wordline, the second bit line, and a third memory cell between the secondword line and the second bit line; and a fourth cell block including thesecond bit line, the third word line, and a fourth memory cell betweenthe second bit line and the third word line, wherein each of the firstthrough fourth memory cells includes a memory unit and a switching unit,and the switching unit includes Ovonic threshold switching (OTS)devices.
 18. The memory device of claim 17, wherein each of the firstthrough fourth memory cells includes an inclined sidewall, a top surfaceof each of the first through fourth memory cells has a first width inthe first direction, a bottom surface of each of the first throughfourth memory cells has a second width in the first direction, and thesecond width is greater than the first width.
 19. A memory devicecomprising: a first word line driving region and a second word linedriving region on a substrate; a plurality of first word lines on thefirst and second word line driving regions, the plurality of first wordlines extending in a first direction parallel to a top surface of thesubstrate, each of the plurality of first word lines having a firstlength in the first direction; a plurality of first bit lines on theplurality of first word lines, the plurality of first bit linesextending in a second direction that is parallel to the top surface ofthe substrate and intersecting the first direction; a plurality ofsecond word lines on the plurality of first bit lines, the plurality ofsecond word lines extending in the first direction, the plurality ofsecond word lines being shifted from the plurality of first word linesin the first direction by about ½ of the first length; a plurality ofsecond bit lines on the plurality of second word lines, the plurality ofsecond bit lines extending in the second direction; a plurality ofmemory cells between the plurality of first word lines and the pluralityof first bit lines and between the plurality of second word lines andthe plurality of second bit lines; a plurality of first word linecontacts each extending from bottom surfaces of the plurality of firstword lines to the first word line driving region; and a plurality ofsecond word line contacts each extending from bottom surfaces of theplurality of second word lines to the second word line driving region,the plurality of second word line contacts being shifted from theplurality of first word line contacts in the first direction by about ½of the first length.
 20. The memory device of claim 19, wherein onefirst word line contact among the plurality of first word line contactsis apart from an edge of corresponding first word line among theplurality of first word lines by a first distance in the firstdirection, another first word line contact among the plurality of firstword line contacts, which is the closest to the one first word linecontact, is apart from an edge of corresponding first word line amongthe plurality of first word lines by a second distance in the firstdirection, and the second distance is greater than the first distance.